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/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Core / CSharp / System / Windows / Media / Animation / BounceEase.cs / 1305600 / BounceEase.cs
//------------------------------------------------------------------------------ // Copyright (c) Microsoft Corporation, 2008 // // File: BounceEase.cs //----------------------------------------------------------------------------- using MS.Internal; namespace System.Windows.Media.Animation { ////// This class implements an easing function that can be used to simulate bouncing /// public class BounceEase : EasingFunctionBase { public BounceEase() { } ////// Bounces Property /// public static readonly DependencyProperty BouncesProperty = DependencyProperty.Register( "Bounces", typeof(int), typeof(BounceEase), new PropertyMetadata(3)); ////// Specifies the number of bounces. This does not include the final half bounce. /// public int Bounces { get { return (int)GetValue(BouncesProperty); } set { SetValueInternal(BouncesProperty, value); } } ////// Bounciness Property /// public static readonly DependencyProperty BouncinessProperty = DependencyProperty.Register( "Bounciness", typeof(double), typeof(BounceEase), new PropertyMetadata(2.0)); ////// Specifies the amount of bounciness. This corresponds to the scale difference between a bounce and the next bounce. /// For example, Bounciness = 2.0 correspondes to the next bounce being twices as high and taking twice as long. /// public double Bounciness { get { return (double)GetValue(BouncinessProperty); } set { SetValueInternal(BouncinessProperty, value); } } protected override double EaseInCore(double normalizedTime) { // The math below is complicated because we have a few requirements to get the correct look for bounce: // 1) The bounces should be symetrical // 2) Bounciness should control both the amplitude and the period of the bounces // 3) Bounces should control the number of bounces without including the final half bounce to get you back to 1.0 // // Note: Simply modulating a expo or power curve with a abs(sin(...)) wont work because it violates 1) above. // // Constants double bounces = Math.Max(0.0, (double)Bounces); double bounciness = Bounciness; // Clamp the bounciness so we dont hit a divide by zero if (bounciness < 1.0 || DoubleUtil.IsOne(bounciness)) { // Make it just over one. In practice, this will look like 1.0 but avoid divide by zeros. bounciness = 1.001; } double pow = Math.Pow(bounciness, bounces); double oneMinusBounciness = 1.0 - bounciness; // 'unit' space calculations. // Our bounces grow in the x axis exponentially. we define the first bounce as having a 'unit' width of 1.0 and compute // the total number of 'units' using a geometric series. // We then compute which 'unit' the current time is in. double sumOfUnits = (1.0 - pow) / oneMinusBounciness + pow * 0.5; // geometric series with only half the last sum double unitAtT = normalizedTime * sumOfUnits; // 'bounce' space calculations. // Now that we know which 'unit' the current time is in, we can determine which bounce we're in by solving the geometric equation: // unitAtT = (1 - bounciness^bounce) / (1 - bounciness), for bounce. double bounceAtT = Math.Log(-unitAtT * (1.0-bounciness) + 1.0, bounciness); double start = Math.Floor(bounceAtT); double end = start + 1.0; // 'time' space calculations. // We then project the start and end of the bounce into 'time' space double startTime = (1.0 - Math.Pow(bounciness, start)) / (oneMinusBounciness * sumOfUnits); double endTime = (1.0 - Math.Pow(bounciness, end)) / (oneMinusBounciness * sumOfUnits); // Curve fitting for bounce. double midTime = (startTime + endTime) * 0.5; double timeRelativeToPeak = normalizedTime - midTime; double radius = midTime - startTime; double amplitude = Math.Pow(1.0 / bounciness, (bounces - start)); // Evaluate a quadratic that hits (startTime,0), (endTime, 0), and peaks at amplitude. return (-amplitude / (radius * radius)) * (timeRelativeToPeak - radius) * (timeRelativeToPeak + radius); } protected override Freezable CreateInstanceCore() { return new BounceEase(); } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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